A confocal microscopy image analysis method to measure adhesion and internalization of Pseudomonas aeruginosa...

Formation of multicellular structures such as biofilms is an important feature in the physiopathology of many disease-causing bacteria. We recently reported that Pseudomonas aeruginosa adheres to epithelial cells rapidly forming early biofilm-like aggregates, which can then be internalized into cells. Conventional methods to measure adhesion/internalization, such as dilution plating for total cell-associated or antibiotic protected bacteria, do not distinguish between single and aggregated bacteria. We report a procedure that combining double bacteria labeling, confocal microscopy and image analysis allows identification and quantification of the number of adhered and internalized bacteria distinguishing between single and aggregated bacterial cells. A plugin for Fiji to automatically perform these procedures has been generated.